1. Technical Field
The technical field relates generally to hybrid-electric motor vehicles and, more particularly, to allocation of immediately available power, particularly engine generated power, between propulsion and traction battery charging.
2. Description of the Technical Field
Electrical motors generally exhibit greater operating efficiencies than do internal combustion engines. In addition, internal combustion engines achieve their maximum efficiencies over relatively narrow RPM and torque ranges in comparison to electrical motors. Consequently there is a built in bias in favor of using electrical motors over an internal combustion engine for propulsion on hybrid-electric vehicles and to running internal combustion engines when they can operated at efficient brake specific fuel consumptions.
The bias in favor of using electrical motors is constrained by the inherent limitations of the batteries commonly used to provide a reserve of electrical power. In contrast to the hydro-carbon fuels usually used with internal combustion engines, contemporary batteries have a much higher mass per unit of energy stored. Batteries also exhibit limitations in terms of the rate at which they can be discharged and recharged. If a hybrid-electric vehicle is in use a large proportion of the time and is called on to operate over distances exceeding the capacity of the batteries to carry the vehicle it is unavoidable that the internal combustion engine will be run. The question becomes one of how to run the internal combustion engine in an efficient manner in order to meet vehicle operational goals. These goals can be maximizing vehicle range, minimizing vehicle operating cost for repeated daily operation over a course of fixed length, or minimizing down time for battery recharging.